Antero-postero-stabilized knee prosthesis

Abstract

A prosthesis, such as a knee prosthesis, for the lower limb including a femur prosthetic element having a block presenting a lug running into the trochlea and adjacent to a notch from which a convex bearing surface extends, and a tibia prosthetic element having an insert with a sagittally oriented elevation defining a projection for antero-postero stabilization engaged in the notch when the prosthesis is in the extended position and which runs into a concave sliding ramp that extends to the rear edge of the insert.

What is claimed is:  
     
       1. A knee prosthesis comprising: 
       a U-shaped femur prosthetic element defining a housing for engaging the resectioned epiphysial portion of a femur and comprising an anterior portion defining a trochlea on its front face and a distalo-posterior portion defining two condyles between which said portion forms a block presenting, in its outer face relative to the housing, a lug connected to the trochlea and adjacent to a notch from which a convex bearing surface extends to the rearmost portion of the block; and  
       a tibia prosthetic element comprising a base for fitting to the resectioned epiphysial portion of a tibia, and an insert mounted on the base and presenting, facing the femur prosthetic element, two glenoid cavities for co-operating with the condyles, said element including between the glenoid cavities an elevation of sagittal orientation co-operating with the front edge of said insert to define a projection for antero-posterior stabilization which is engaged in the notch in the extended position of the prosthesis and which is connected to a concave sliding ramp extending to the rear edge of the insert and co-operating with the convex portion facing it in the extended position of the prosthesis to define a gap of section that increases from the zone where the projection and the notch are in contact all the way to said rear edge,  
       wherein the convex bearing surface is defined by:  
       a transverse radius of curvature R t  of center O occupying an angular extent a t ; and  
       a sagittal curve made up of:  
       à a substantially middle portion of radius R 35 , of center O, and occupying an angular extent a 35 ;  
       à a front portion connecting the middle portion to the notch, having a radius R 34 , a center O 1  situated beyond and beneath the center O relative to the anterior portion of the prosthetic element, and occupying an angular extent a 34 ; and  
       à a rear portion having a radius R 36 , a center O 2  situated beyond and beneath the center O relative to said anterior edge, and occupying an angular extent a 36 .  
     
     
       2. A prosthesis according to  claim 1 , comprising a femur prosthetic element and a tibia prosthetic element whose concave sliding ramp includes: 
       a transverse radius of curvature R c , a center O, and occupying an angular extent a c ; and  
       a sagittal curve made up of:  
       à a front portion extending from the projection with a radius R 43 , a center O, and occupying an angular extent a 43 ; and  
       à a rear portion extending the front portion to the rear edge of the insert and possessing a radius R 44 , a center O 3  situated beneath the center O, and occupying an angular extent a 44 .  
     
     
       3. A prosthesis according to  claim 1 , comprising a tibia prosthetic element and a femur prosthetic element in which: 
       the radius R t  possesses a length lying in the range 14 mm to 18 mm;  
       the radius R 34  possesses a length lying in the range 12.4 mm to 17 mm;  
       the radius R 35  possesses a length lying in the range 17.7 mm to 24.4 mm;  
       the radius R 36  possesses a length lying in the range 14.6 mm to 20.1 mm;  
       the angular extent a t  occupies an angle lying in the range 70.64° to 80.87°;  
       the angular extent a 33  occupies an angle lying in the range 22.75° to 22.75°;  
       the angular extent a 34  occupies an angle of 70°; and  
       the angular extent a 35  occupies an angle lying in the range 89.05° to 91.67°.  
     
     
       4. A prosthesis according to  claim 1 , wherein the radius R 35  is of center O known as the “reference” center, as is the radius R 35 , whereas the radius R 34  is of center O 1  situated beyond and beneath the reference center and the radius R 36  is of center O 2  situated beyond and beneath the center O. 
     
     
       5. A prosthesis according to  claim 1 , comprising a femur prosthetic element and a tibia prosthetic element in which: 
       the radius R c  possesses a length lying in the range 16 mm to 20 mm;  
       the radius R 43  possesses a length lying in the range 17.77 mm to 24.4 mm;  
       the radius R 44  possesses a length lying in the range 16.5 mm to 20.5 mm;  
       the angular extent a c  occupies an angle lying in the range 57.42° to 64.72°;  
       the angular extent a 43  occupies an angle lying in the range 75.51° to 76.31°; and  
       the angular extent a 44  occupies an angle lying in the range 35.54° to 40.02°.  
     
     
       6. A prosthesis according to  claim 2 , wherein: 
       the radius R c  is of center O known as the “reference” center;  
       the radius R 43  is of center O; and  
       the radius R 44  is of center O 3 , situated vertically beneath the center O.  
     
     
       7. A prosthesis according to  claim 1 , wherein the convex portion of the concave femur prosthetic element and the sliding ramp of the tibia prosthetic element are formed by surface portion of pseudo-cylindrical nature, and wherein the insert is mounted on the base via a pivot. 
     
     
       8. A prosthesis according to  claim 7 , wherein the bearing surface is defined by: 
       a front portion having a sagittal radius of curvature R 51  of center O and occupying an angular extent a 51 ; and  
       by a rear portion following the front portion and possessing a sagittal radius of curvature R 52 , of center O 4 , and occupying an angular extent a 52 .  
     
     
       9. A prosthesis according to  claim 8 , wherein: 
       the radius R 51  possesses a length lying in the range 15.05 mm to 20.75 mm;  
       the radius R 52  possesses a length lying in the range 13.3 mm to 18.3 mm;  
       the angular extent a 51  occupies an angle lying in the range 87.28° to 89.67°; and  
       the angular extent a 52  occupies an angle lying in the range 90.76° to 98.47°.  
     
     
       10. A prosthesis according to  claim 7 , wherein the concave sliding ramp is defined by a radius of curvature R 53  of center O occupying an angular extent a 53 . 
     
     
       11. A prosthesis according to  claim 10 , wherein: 
       the radius R 53  possesses a length lying in the range 15.05 mm to 20.75 mm; and  
       the angular extent a 53  occupies an angle lying in the range 98.46° to 102.6°.